1. Field of the Invention
This invention relates generally to the field of atomic force microscopy. More particularly, it relates to an atomic force microscopy system and method for imaging properties using currents induced within the sample material.
2. Description of the Related Art
Atomic force microscopy (AFM) is a type of scanning microscopy that provides high resolution, three-dimensional imaging at the atomic and molecular level. A cantilever terminating in a sharp, pointed tip is scanned across the surface of a sample, either in contact with or at a predetermined distance above the sample surface. A laser beam is focused on a portion of the cantilever during scanning, and a photodiode detector or other suitable detector collects the reflected light in order to detect minute deflections of the cantilever as the tip interacts with the sample surface. AFM is capable of measuring very small forces (less than 1 nanonewton) present between the tip and the sample surface and can be used to image surface topography as well as various physical properties of the sample.
To measure electric and dielectric properties, many currently available AFM techniques apply a bias voltage between a conductive tip and the sample. These devices require a tip made of conductive material and a bias voltage supply and setup. In addition, the voltage between the tip and the sample may become too high, causing damage to the sample. The application of a bias voltage to the sample may also alter the properties of many types of samples. Soft sample materials such as powders or biological materials are particularly prone to damage and alteration, which limits imaging of these materials.
Currently available AFM techniques that measure magnetic and ferroelectric properties have similar drawbacks. Most conventional magnetic force microscopy (MFM) systems require the use of a tip comprising magnetic material and a stiff cantilever having a spring constant of 2-40 Newtons/meter (N/m) or higher. The cantilever is coupled to an oscillator and vibrated a few nanometers above the magnetic sample. Based on interactions between the magnetic tip and the sample surface, the magnetic properties of the sample may be determined without the tip coming into contact with the sample surface. However, the resolution and sensitivity of MFM is generally poor as compared to other methods of AFM because the required stiffness of the cantilever and imaging in non-contact mode prevents the system from being as responsive to minor changes. This reduced responsiveness results in lower sensitivity and a poor quality, low resolution image. Increasing the magnetic field surrounding the tip increases the resolution but it may also affect the magnetization of the sample.